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JeffNEWS, July 12, 1994
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Jeff Researchers Find Evidence for Gene on Chromosome 18
That Increases Risk for Manic Depressive Illness in Some Families
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Jefferson researchers have identified genetic markers on chromosome
18 for a gene that increases the risk for manic depressive illness.
While the research does not provide any immediate implications for the
clinical diagnosis or treatment of manic depressive illness, the
finding, published in the June 21 issue of the Proceedings of the
National Academy of Sciences (PNAS), is a major step forward because it
defines a specific area of chromosome 18 as essential to the genetic
origins of this common and devastating illness.
Manic depressive illness, also known as bipolar illness, is a mood
disorder in which patients experience recurring and unpredictable mood
swings, from deep despair and depression to highly excited euphoria.
"It is a complex disease both clinically and genetically," says Wade
Berrettini, MD, PhD, professor of psychiatry and lead author of the
study. "The disorder varies tremendously in its intensity and duration
of mood swings. Some patients' moods alternate repeatedly over a period
of days, while others' moods cycle over a period of months."
In the PNAS study, Jefferson researchers identified a link between
DNA sequences on chromosome 18 and affected family members while
studying the genetic makeup of 22 families with a high incidence of
illness. Of the 400 individuals studied, 170 have bipolar or unipolar
illness. Researchers compared the genetic material of affected relatives
from each family pedigree. In 8 of the 22 families studied, affected
family members shared similarities in a region of chromosome 18 while
unaffected family members did not.
"Our study shows that there is a susceptibility gene for bipolar
illness on chromosome 18 near the 11p region in one-third of the
families studied (8 out of 22)," says Dr. Berrettini.
While the other families did not show clear linkage to chromosome 18,
this discrepancy is consistent with the complex and multifaceted nature
of bipolar illness. "There are undoubtedly multiple genes that increase
the risk for bipolar illness, and there are other genes that have a
protective effect," says Dr. Berrettini. "Many of these genes are
probably genes of partial effect, which means that several genes need to
be inherited in the right combination before the disease becomes
clinically apparent. We don't understand enough about the causes of
bipolar illness to describe exactly what all of these factors are, but
we know that both genetic and environmental factors exist."
"We are hopeful", says Dr. Berrettini, that the genetic approach will
help us better understand the biochemistry of bipolar illness so that we
can develop more targeted approaches to controlling the disorder."
Thomas N. Ferraro, PhD, assistant professor of psychiatry at
Jefferson, also contributed to this study.
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